Research Article Volume 3 Issue 4 - February 2018 DOI: 10.19080/CERJ.2018.03.555617 Civil Eng Res J Copyright © All rights are reserved by Afshin Kalantari Seismic Vertical Component Effects on Seismic Demands of a Base Isolated Bridge with Friction- Rubber Bearings Afshin Kalantari* and Seyyed Amirhossein Moayyedi International Institute of Earthquake Engineering and Seismology, Iran Submission: November 18, 2017; Published: February 26, 2018 *Corresponding author : Afshin Kalantari,Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology, Iran, Tel:22830830; Email : Introduction The growth of urban population and industrial activities and their steadily increasing transportation requirements have led to a widespread construction and use of highway structures in and around major cities. Bridges play an essential role in transportation networks specify after earthquakes. Given the vital role of these structures in transportation systems, ensuring their safety and optimal seismic performance is of significant importance. Base isolation systems can protect the superstructure against earthquake damage by decoupling it from the substructure and thus from the seismic load. Such seismic load reduction scheme largely depends on proper function of isolation units. Thus, factors associated with the performance of isolators are of significant importance for the seismic performance of structure and have to be evaluated under different seismic excitation. Vertical components and strong pulse motion of ground motions are among the factors that may adversely affect the performance of a bridge isolation system, especially in near-fault areas. In particular, this component can undermine the performance of friction isolators operating alone or in combination with rubber bearings. In such isolators, variation in axial force between the two sliding pads may induce instability in the energy dissipation process and cause erratic isolation performance, and thereby affect the relative displacement and shear response of the device and structure. Figure 1 shows a friction-rubber hybrid bearing in a bridge with box girder deck. The effects of vertical seismic component on bridges with or without seismic isolation systems have been extensively researched. Some of these studies have emphasized the consequences of ignoring the vertical component in the near- fault structures. Papazoglou & Elnashai [1] have provided both analytical and field evidence supporting the damaging effects of vertical seismic component on buildings and bridges. They expressed that significant fluctuation in the axial force of vertical components leads to a reduction in the shear capacity Civil Eng Res J 3(4): CERJ.MS.ID.555617 (2018) 0092 Abstract Past experiences regarding the near-fault effect of earthquakes have shown a potentially significant effect of vertical component on the response of bridges and their seismic equipment. In this study, a friction-rubber hybrid isolator was designed for a highway bridge and modeled to evaluate the effect of vertical seismic component on the performance of isolators in a concrete bridge. Numerical study on the bridge was conducted under two conditions: i. With only two horizontal seismic components, and ii. With three seismic components (including the vertical component). For this purpose, finite element model of the structure was developed in Open Sees software and then subjected to nonlinear dynamic analysis under 29 different ground motion records. The results showed that maximum shear and axial force in the isolator elements undergo significant increase under all seismic excitations. Due to the absence of self-restoring force in the studied isolator, the permanent and maximum deck displacement increased during some of the earthquake records, and in a few cases, the permanent displacements of the deck were particularly significant. The axial forces of the isolators on the base and abutment were found to be correlated with the spectral acceleration at the period of vibration mode effective in vertical direction. Keywords: Seismic isolation; Vertical component; Time history analysis; Highway bridge